Lubricant oils include industrial gear oil, engine oil, lubricant oil for fibers, lubricant oil for rolling and lubricant oil for refrigerators.
As the working conditions for various industrial machines become severe recently, industrial gear oil has come to be required to maintain its lubricating properties and detergency at high temperature. In particular, improved lubricating properties and detergency have come to be required of the industrial gear oil used in the processes for thermosetting coating or baking food. There have heretofore been used lubricant oils of a synthetic hydrocarbon type, a carboxylic acid ester type or a glycol type.
Synthetic hydrocarbon oil and carboxylic acid ester oil, however, are still insufficient in lubricating properties, and, in addition, they have such a drawback that they cannot be used as lubricant oil at high temperature because they form carbide when heated over a long period of time. On the other hand, though glycol lubricant oil is advantageous in that it does not form much carbide when heated over a long period of time, it has insufficient lubricating properties and high hygroscopicity. Accordingly, improvement thereof has been desired.
Engine oil has been required to have lubricating properties and dispersancy at higher temperature over a longer period to cope with improved performance of automotive engines. When addition of the additives for the engine oil is attempted to respond to such a requirement, it results in an increase in the additives. The increase in the amount of additive induces harmful results such as precipitation or deposition of mayonnaise sludge. Though there has heretofore been tried the use of mineral oil in combination with synthetic hydrocarbon oil or carboxylic acid ester oil, the resultant base oil shows both insufficient lubricating properties and dispersancy when used at high temperature over a long period of time. Lubricant oil for 2-cycle engines, different from that for the above-mentioned automobile engines, that is, 4-cycle engines, is burnt after it is added to gasoline due to the mechanism of the engines, and therefore its detergency is especially important. Though castor oil, polybutene and the like have been used as lubricant oil for 2-cycle engines, both their lubricating properties and detergency are insufficient.
Gear oil for automobiles, especially for ATF is required to have a low friction coefficient and decreased change thereof with the lapse of time. Antifriction agents and friction-adjusting agents have therefore been used. Automotive gear oil containing these additives has a problem that the friction coefficient thereof increases with time.
As a lubricant oil for fibers, carboxylic acid ester lubricant oil and glycol lubricant oil have usually been employed, but they cannot simultaneously satisfy lubricating properties and detergency.
Lubricant oil containing tallow as its main ingredient has been conventionally used as rolling lubricant oil. In spite of its highly lubricating properties and excellent rolling efficiency, such lubricant oil is extremely poor in detergency, and hence it requires a process for washing the remaining tallow. Though carboxylic acid ester lubricant oil has been used as rolling lubricant oil, it shows little practicality due to poor lubricating properties, despite its significantly excellent detergency.
With the alteration of a refrigerant gas for refrigerators to Freon R-134a (CH.sub.2 F-CF.sub.3) which is an ozone layer-nondestructive HFC, mineral oil and alkylbenzenes, which heretofore have been used for lubricant oil for refrigerators, have come not to be used therefore because they have no mutual solubility with the refrigerant gas. Glycol ether type lubricant oil has currently been developed for the lubricant oil for refrigerators where the above-mentioned refrigerant is used.
For example, U.S. Pat. No. 4,755,316 discloses a compression refrigerator composition composed of tetrafluoroethane and a polyoxyalkylene glycol having a molecular weight of 300 to 2,000 and a kinematic viscosity at 37.degree. C. of about 25 to 150 cSt.
Such glycol ether lubricant oil, however, generally has insufficient thermal stability and high hygroscopicity, and in addition it has been pointed out that the glycol ether lubricant oil has such a drawback that it shrinks rubber sealing materials such as nitrile rubber (NBR) and increases their hardness.
U.S. Pat. No. 3,627,810 discloses a process for preparing carbonates of higher alcohols represented by the formula R'OCOOR", and the carbonates are described to be useful as hydraulic oil, lubricant oil and plasticizers. The specification, however, does not clearly describe their concrete use, for example, for lubricant oil for refrigerators, especially refrigerator lubricant oil excellent in mutual solubility with ozone layer-nondestructive Freon. In the above formula, R' and R" are each a higher alcohol residue.
U.S. Pat. No. 3,657,310 discloses a process for preparing carbonates represented by the formula ROCOO(AO).sub.n R'. Though these carbonates are described to be useful as lubricant oil, hydraulic oil and plasticizers, their concrete use, for example, for lubricant oil for refrigerators, especially refrigerator lubricant oil excellent in mutual solubility with ozone layer-nondestructive Freon. In the above-mentioned formula, R and R' each denote a monovalent aliphatic group, and A indicates an alkylene group having 2 to 4 carbon atoms, with n denoting an integer of not less than 1.
European Patent No. 089,709 discloses a process for preparing a carbonate of a higher alcohol by ester interchange reaction between a higher alcohol having a molecular weight of 100 to 270 and an alcohol carbonate having a low boiling point, and a lubricant oil composition containing such a carbonate of a higher alcohol.
Japanese Patent L-O-P No. 37,568/1973 discloses a motor transmitting liquid containing at least one carbonate represented by the general formula EQU R.sup.1 O--X--OCOO).sub.n X--OR.sup.2
wherein R.sup.1 and R.sup.2 are each independently hydrogen, an aliphatic group, an aromatic-substituted aliphatic group, an aromatic group, an acyl group, an alkoxycarbonyl group or an aryloxy group, n is a number of 1 to 10, and X is an alkylene group having at least two carbon atoms in the main molecular carbon chain, the molecular chain optionally containing a cycloalkylene group, an aralkylene group, an arylene group or at least one hetero atom. The use of the carbonate esters disclosed in the publication, however, are for transmitting liquid and not for lubricant oil.
Furthermore, Japanese Patent Publication No. 4727/1971 discloses a process for preparing polyethylene glycol monomethyl ether carbonates represented by the general formula EQU CH.sub.3 --OCH.sub.2 CH.sub.2).sub.x OCOO--CH.sub.2 CH.sub.2 O).sub.y CH.sub.3
wherein x and y are each 2 or 3.
The publication teaches that the polyethylene glycol monomethyl ether carbonates described above are useful for the preparation of a brake liquid, and they are also useful as synthetic lubricants. However, it does not clearly describe concrete use, for example, lubricant oil for refrigerators, especially refrigerator lubricant oil excellent in mutual solubility with ozone layer-nondestructive Freon.
The present invention is intended to solve the above-described problems involved in the prior art method, and an object of this invention is to provide a lubricant oil composition having excellent lubricating properties and detergency, and also having excellent mutual solubility with ozone layer-nondestructive Freon such as Freon R-134a.